1. Field of the Invention
The present invention relates to the field of high frequency transconductance amplifiers.
2. Prior Art
There are at least three kinds of high frequency amplifiers: (1) conventional, (2) current feedback (transimpedance) and (3) transconductance amplifiers. Conventional amplifiers have high gain and good DC characteristics, but they have limited bandwidth (if they are unity-gain stable) and their gain-bandwidth product tends to be constant. Transimpedance amplifiers have lower gain, but higher bandwidth. Their DC performance is usually poor, and they usually have asymmetric inputs, but their bandwidth is fairly independent of gain. Transconductance amplifiers can have high bandwidth, but only if feedback is kept to a minimum. Their transconductance is usually set by a current, and the actual transconductance varies with process and temperature. To get any accuracy, one must use feedback, and this tends to slow the transconductance amplifiers down. However, since their transconductance can be programmed with a current, they can be made into variable gain amplifiers. However, their differential input voltage range is limited, and this usually confines them to current input designs (Norton amplifiers).